chore(db): add playbook versioning migration

apps/api/migrations/adr104_playbook_versioning.sql

@@ -0,0 +1,20 @@
+-- ADR-104 T4: Playbook versioning / lineage schema
+-- 2026-04-30 Codex: LLM-generated Playbooks must preserve lineage instead of
+-- overwriting prior operational knowledge.
+
+ALTER TABLE playbooks
+    ADD COLUMN IF NOT EXISTS version INTEGER NOT NULL DEFAULT 1,
+    ADD COLUMN IF NOT EXISTS parent_playbook_id VARCHAR(36),
+    ADD COLUMN IF NOT EXISTS supersedes_playbook_id VARCHAR(36),
+    ADD COLUMN IF NOT EXISTS version_reason TEXT;
+
+UPDATE playbooks
+SET parent_playbook_id = playbook_id
+WHERE parent_playbook_id IS NULL;
+
+CREATE INDEX IF NOT EXISTS ix_playbook_lineage
+    ON playbooks(parent_playbook_id, version);
+
+CREATE INDEX IF NOT EXISTS ix_playbook_supersedes
+    ON playbooks(supersedes_playbook_id)
+    WHERE supersedes_playbook_id IS NOT NULL;